# 键值对存储演练 ## Prerequisite: enabling JetStream If you are running a local `nats-server` stop it and restart it with JetStream enabled using `nats-server -js` (if that's not already done) You can then check that JetStream is enabled by using ```shell nats account info ``` ``` Connection Information: Client ID: 6 Client IP: 127.0.0.1 RTT: 64.996µs Headers Supported: true Maximum Payload: 1.0 MiB Connected URL: nats://127.0.0.1:4222 Connected Address: 127.0.0.1:4222 Connected Server ID: ND2XVDA4Q363JOIFKJTPZW3ZKZCANH7NJI4EJMFSSPTRXDBFG4M4C34K JetStream Account Information: Memory: 0 B of Unlimited Storage: 0 B of Unlimited Streams: 0 of Unlimited Consumers: 0 of Unlimited ``` If you see the below instead then JetStream is *not* enabled ``` JetStream Account Information: JetStream is not supported in this account ``` ## Creating a KV bucket Just like you have to create streams before you can use them, you need to first create a 'KV bucket' using `nats kv add `: ```shell nats kv add my_kv ``` ``` my_kv Key-Value Store Status Bucket Name: my_kv History Kept: 1 Maximum Bucket Size: unlimited Maximum Value Size: unlimited Bucket Location: unknown Values Stored: 0 Backing Store Name: KV_my_kv ``` ## Storing a value Now that we have a bucket, we can use it to 'put' (store) values at keys: ```shell nats kv put my_kv Key1 Value1 ``` which should return `Value1` ## Getting a value Now that we have value stored at key "Key1" we can retrieve that value with a 'get': ```shell nats kv get my_kv Key1 ``` ``` my_kv > Key1 created @ 12 Oct 21 20:08 UTC Value1 ``` ## Deleting a value You can always delete a Key/Value entry by using `nats kv del my_kv Key1` ## Watching a K/V Store A functionality (normally not provided by Key/Value stores) is available with the NATS KV Store is the ability to 'watch' a bucket (or a particular key in that bucket) and receive real-time updates to changes in the store. For example run `nats kv watch my_kv`: this will start a watcher on the bucket we have just created earlier. If you followed this walkthrough the last operation that happened on the key is that it was deleted. Because by default the KV bucket is set with a history size of one (i.e. it keeps only the last change) and the last operation on the bucket was a delete of the value associated with the key "Key1" that is the only thing that get received by the watcher: ```shell nats kv watch my_kv ``` ``` [2021-10-12 13:15:03] DEL my_kv > Key1 ``` Keep that `nats kv watch` running and in another window do another 'put' ```shell nats kv put my_kv Key1 Value2 ``` As soon as that command is run you will see that put event received by the watcher: ```shell [2021-10-12 13:25:14] PUT my_kv > Key1: Value2 ``` ## Cleaning up Once you are finished playing, you can easily delete the KV bucket and release the resource associated with it by using: ```shell nats kv rm my_kv ``` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.natsclub.cn/cn/nats-gai-nian/jetstream/key-value-store/kv_walkthrough.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.